Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session S13: Convection and Buoyancy-driven Flows: Free Convection |
Hide Abstracts |
Chair: Olga Shishkina, Max-Planck Institut Room: 304 |
Tuesday, November 26, 2019 10:31AM - 10:44AM |
S13.00001: Multiscaling analysis of buoyancy-driven turbulence in a differentially heated vertical channel Tie Wei A multiscaling analysis is presented for the turbulent flow and heat transfer in a differentially heated vertical channel (DHVC). Based on the characteristics of force balance, a three-layer structure is proposed for the mean momentum balance (MMB) equation. In Layer I, a viscous inner layer adjacent to the wall, the force balance is between the viscous force and the buoyancy force. In Layer III, the outer layer, the force balance is between the Reynolds shear force and the buoyancy force. A multiscaling analysis of the MMB equation is developed for the inner and outer layers. A proper scale for the Reynolds shear stress is found to be $u_\tau U_\mathrm{max}$ where $u_\tau$ is the friction velocity and $U_\mathrm{max}$ is the maximum streamwise velocity. The structure for the mean heat (MHB) equation equation can also be divided into three layers based on the characteristics of the diffusional and turbulent heat flux. The outer scaling of the MHB equation in a DHVC is similar to passive scalar transport in forced convection. However, the inner scaling for the thermal inner layer in a DHVC is distinctly different from that in forced convection. The multiscaling analysis of the MMB and MHB equations agree well with the direct numerical simulation data of DHVC. [Preview Abstract] |
Tuesday, November 26, 2019 10:44AM - 10:57AM |
S13.00002: Superstructures in turbulent thermal convection in slender cells Olga Shishkina, Lukas Zwirner The large scale circulation (LSC) is one of the most important features in turbulent natural thermal convection. It is self-organized, has its own complicated dynamics and plays a key role in the global heat and momentum transport in convective systems. In this study, we analyze the LSC properties in turbulent Rayleigh--Benard convection and inclined convection of small-Prandtl-number fluids in slender geometries (cylindrical containers of the diameter-to-height aspect ratios smaller than one). We investigate in detail the structures of the so-called single-roll and multiple-roll LSCs, their strength and path lengths and their relation to the strength of the volume-averaged heat transport in the system. The problems of the LSC extraction in experiments and numerical simulations and interpretation of the different LSC modes will be also discussed. [Preview Abstract] |
Tuesday, November 26, 2019 10:57AM - 11:10AM |
S13.00003: Turbulent natural convection in a cavity with a free surface under non-Oberbeck-Boussinesq conditions William Hay, Miltiadis Papalexandris Turbulent natural convection of liquids is encountered in many environmental and industrial applications. For example, in the oceans, the buoyant flow of water due to temperature and concentration gradients has been studied extensively over the years. More recently, highly turbulent flows of a similar nature are being studied to better understand thermal mixing in nuclear spent fuel pools under accidental conditions. In such a case, the Rayleigh number can be as high as $10^{14}$. Moreover, due to significant temperature variations, the water transport properties can no longer be considered as constant. Therefore, the validity of the Oberbeck-Boussinesq approximation for the flows of interest becomes questionable. In this talk we present results from both direct numerical and large-eddy simulations of a cuboid domain, periodic in the longitudinal direction, with a free-slip upper boundary and with water as the working fluid under non-Oberbeck-Boussinesq conditions. Over a series of simulations at increasing Rayleigh number we assess the impact of the free-slip boundary and variable fluid properties on the turbulent flow statistics. [Preview Abstract] |
Tuesday, November 26, 2019 11:10AM - 11:23AM |
S13.00004: Influence of shroud$-$chimney configuration on heat transfer from horizontal cylinder: Experimental and numerical investigation. Ghalib Y. Kahwaji, Mohamed A. Samaha, Omar Ali, Mohanad Taha Ali In our prior study, the novel shroud$-$chimney configuration SCC (semicircular shrouds and expended chimney) has been numerically demonstrated to passively augment natural convection heat transfer from a horizontal cylinder. However, in order to implement such a configuration for practical utilizations, the heat flow properties must be experimentally observed and understood. In this work, well-controlled experiments are carried out to show the impact of SCC on the heat transfer from a horizontal cylinder subjected to constant measured heat fluxes. Circumferential temperature measurements at the cylinder surface, shrouds and ambient are performed using thermocouples. The emissivity of the cylinder is measured using a thermal camera that is needed for estimating the heat radiation. All presented cases are numerically simulated for validation. The measurements show that SCC promotes the convection heat transfer from the cylinder agreeing well with the numerical results. This validates the capability of this simple inexpensive passive method for practical uses. Furthermore, a parametric study is presented to show the optimum range of the design parameters for the best SCC performance. [Preview Abstract] |
Tuesday, November 26, 2019 11:23AM - 11:36AM |
S13.00005: Turbulent thermal convection: the differential heating effects Philipp Reiter, Rodion Stepanov, Olga Shishkina A significant class of geophysical and astrophysical flows are excited by temperature variations along a surface of the fluid layer. Using 3D direct numerical simulations, we study the effects of different temperature and velocity boundary conditions in Rayleigh-Benard convection and horizontal convection, under the requirement that the area-averaged temperatures of the heated and cooled plates are kept constant. For these systems we analyze the global flow structures and the heat transport and investigate their dependences on the particular parameters of the boundary conditions. To explain our findings, we exploit a decomposition of the flow fields into the mean and fluctuation components. For some configurations (in horizontal convection) we also extract different Rayleigh-number regimes and present stability thresholds above which the flow exhibits characteristic global structures and give theoretical explanations for the underlying mechanisms of these structures. [Preview Abstract] |
Tuesday, November 26, 2019 11:36AM - 11:49AM |
S13.00006: The Effect of Horizontal Buoyancy on Turbulent Thermal Convection Lu ZHANG, Ke-Qing XIA We study the effect of horizontal buoyancy on heat transport in turbulent thermal convection system. Experimentally, a condition of increasing horizontal buoyancy ($Ra_H=\alpha g\sin\beta\Delta H^3/\nu\kappa$) under fixed vertical thermal driving strength ($Ra_V=\alpha g\cos\beta\Delta H^3/\nu\kappa$) is achieved by simultaneously titling the convection cell by an angle $\beta$ and increasing the imposed global temperature difference $\Delta$. Furthermore, we propose a vector formed Nusselt number $\textbf{\textit{Nu}}$ to quantify the global heat transport. For fixed vertical buoyancy, we find that the vertical heat transport increase monotonically with the horizontal buoyancy and the horizontal heat transport is also non-negligible. We also conduct direct numerical simulations, the results of which confirm our experimental findings and highlights the richness in convective transport. [Preview Abstract] |
Tuesday, November 26, 2019 11:49AM - 12:02PM |
S13.00007: Numerical analysis of 3-D laminar natural convection heat transfer from solid vertical cylindrical heat sinks with straight longitudinal fins and comparison with horizontal heat sinks of the same configuration Dibyendu Konar, Shubham Mishra, Mohammad Asif Sultan, Vidyadhar Karlapalem, Subhransu Roy Of the various challenges facing the electronics industry, keeping components cool is utmost important, since overheating reduces the reliability and operating life of a device. Among various cooling methods, natural convection has been deemed fit owing to its distinctive advantages over forced convection. Longitudinal fins are generally used for vertical cylindrical heat sinks since the geometry eases air flow between successive fins. In the present study, CFD analysis of conjugate natural convection from such heat sinks have been carried out in the laminar regime. 15 different heat sinks modelling heat sinks of LED bulbs of dimensions obtained from literature have been developed. Effect of non dimensional fin spacing, fin length and Rayleigh number on the thermal resistance of the heat sink have been studied and values compared with those of horizontal sinks available in literature. It is observed that compared to the horizontal sink, the thermal resistance of the vertical sink is decreased by different percentages for different configurations. Contour plots to capture temperature profiles around the vertical heat sink have been developed. Correlations for Nusselt number have been formulated which are found to show appreciable agreement with computational data. [Preview Abstract] |
Tuesday, November 26, 2019 12:02PM - 12:15PM |
S13.00008: Linear stability analysis of radiatively-driven convection in a lake Todd Christopher, Wilfried Coenen, Stefan Llewellyn Smith Observations of springtime warming of ice-free Lake Superior show that an instability arises each day at the surface and propagates down though the water column on a time scale of hours before restratification occurs at night. This situation is modeled using the Boussinesq approximation, leading to a Rayleigh-Benard-like configuration, except with a periodically-varying forcing term to capture the diurnal heat flux into the system. The forcing term is considered first as either a varying temperature or a varying heat flux at the boundary, but radiative heating in the bulk of the fluid is also investigated. A linear stability analysis of the system leads to a Floquet differential equation eigenvalue problem for the critical Rayleigh number. This problem is solved using a pseudospectral numerical method. The results found agree with the literature where applicable, while extending previous work to cover different boundary conditions and different forms for the forcing term. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2022 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700